Competition for tracer 15N in tussock tundra ecosystems

The objectives of this study were to assess the roles of plant species, time, and site on competition for tracer ¹⁵N (without carrier) in tussock tundra ecosystems. Six experimental sites were located in northern Alaska. After one year across the experimental sites, the recovery of ¹⁵N by litter (11.3–16.3%) and mosses (5.4–16.4%) was significantly greater than for aboveground vascular plants (2.6-5.0%). ¹⁵N recoveries by tundra vascular plants (2.6–5.0%) were low when compared to forest trees (9–25%) which suggest that competition for nitrogen is particularly severe in these cold-dominated tundra ecosystems. There were no significant differences among sites in ¹⁵N recoveries by vascular plants, by mosses, or by litter. There was a statistically significant decline in ¹⁵N recovery with time for Vaccinium vitis-idaea and Eriophorum vaginatum between the second and third year. The shallow rooted Vaccinium vitis-ideae was more highly labeled than the deep rooted Eriophorum vaginatum . Nearness to the source of the applied ¹⁵N played a critical role in competition for surface applied nitrogen.